1. Field of the Invention
The invention relates to a device to protect the image sensor area of a digital still camera from harmful light leakage, which mainly comes through the gap between the camera front and the periphery-surface of the lens barrel, using a simple one-piece part made of black elastic materials such as rubber or elastic plastic.
2. Background Art
The lens of a conventional type of still cameras like 35 mm format has a light leakage prevention means, which is usually made of black fluffy cloth and placed around the rim-edge of the hole, through which the lens moves in and out of the camera front cover, and the periphery-surface of the lens barrel touches the light leakage prevention means while the lens is moving in and out, so that the light cannot come into the film area through the gap between the lens barrel and the front cover rim-edge.
Specifically, for example, FIG. 1 shows the light leakage prevention means, of a conventional still camera of 35 mm format, fixed around the rim-edge of the hole provided on a camera front cover (13), through which lens moves in and out (as shown by arrows) of the camera front cover (13). The light leakage prevention means (11) is made of black fluffy cloth, and fixed on the rim-edge of the hole (12) of the camera front cover (13). The camera front cover (13) covers the front area of an inner camera assembly including a lens barrel (14), and the lens barrel (14) comes out of the front cover (13) through the hole (12) provided on the camera front cover (13) over the lens front, and the lens barrel (14) moves in and out through the hole (12) having practically no gap between the periphery-surface (15) of a lens barrel and the light leakage prevention means (11). While the lens barrel, (14) is moving in and out, the black fluffy cloth of the light leakage prevention means (11) keeps close contact with the periphery-surface (15) of the lens barrel so that no light can come in through the gap between the periphery-surface (15) of the lens barrel and the light leakage prevention means (11).
Such kind of light leakage prevention means, as theretofore mentioned, can be arranged to conventional still cameras, because the lens barrel assembly is driven with sufficiently strong force to override the friction between the lens barrel and the light leakage prevention means (11).
On the contrary, in the case of digital still cameras, lenses are far much smaller and lighter in size and weight than ordinary still camera lenses, and furthermore, the stroke (moving distance) of focusing is extremely short. Consequently, the lens must be driven with very small amount of force and very delicately in comparison with ordinary still cameras. So, if such light leakage prevention means made of black fluffy cloth as the one used in ordinary still cameras is provided for digital still camera lenses, the lens cannot move smoothly because of being overcome by the friction between the periphery-surface of the lens barrel and the light leakage prevention means. For the digital still camera lenses, it is necessary to have some other means of light leakage prevention without having anything that generates strong resistance between the lens barrel and its holder.
In this invention a simple one-piece part is provided to prevent the image sensor area of a digital still camera from receiving harmful light leakage coming into the image sensor area, and to get the image sensor to receive only the light coming through the rearmost element of the lens as described hereinafter.
A lens is usually assembled on a lens assembly base, where the supporting means of a lens barrel is fixed. A light leakage prevention device is formed as a one-piece part and is made of certain black color and light-shielding elastic materials such as rubber or elastic plastic. The upper circle rim-edge of the light leakage prevention device is fixed over the bottom circle rim-edge of the lens barrel. The lower circle rim-edge of the light leakage prevention device is fixed light-tightly on the lens assembly base, where the image sensor is placed underneath of the rearmost element of the lens. Thanks to the elasticity of the material of the light leakage prevention device, the lens can move easily back and forth even though the upper circle rim-edge of the light leakage prevention device is connected to the lens bottom circle rim-edge, and the lower circle rim-edge of the light leakage prevention device is fixed on the lens assembly base. Also thanks to the light-shielding material of the light leakage prevention device, light cannot come through the light leakage prevention device. In other words, the bottom of the lens barrel, together with the light leakage prevention device, cover the entire area of an image sensor, and only the light coming through the rearmost element of the lens can reach the image sensor, keeping a free movement of the lens back and forth.
By using this simple one-piece part made of elastic and light-shielding materials, like black rubber or black elastic plastic, it is possible easily to prevent the digital camera image sensor area from receiving any harmful light, except the light coming through the rearmost element of the lens.